1. Field of the Invention
The invention relates to load or applied force measuring devices, and particularly to a parallel beam system for measuring the displacement of one beam in relation to a stable beam.
2. Description of the Prior Art
Measurement of applied forces and loads are often made with load cells of various configurations that are implemented with bonded metal foil or semiconductor strain gauges. This is a well-developed technology and works very well in many applications. A necessary characteristic of strain gauges is that they be tightly bonded to the load cell mechanisms with a very thin, hard, glue line. They also must be bonded to the load cell in a high stress field (large strain) for adequate sensitivity.
In dynamic loading applications such as are found in "on board" weight scale systems for trucks, forklifts and other material handling equipment, strain gauge systems have exhibited poor reliability. This is due to failure of the hard bonding material under the continual high-stress flexure of the load cells.
Optical position-sensing systems using photodiodes and other light sensitive devices are also well documented in the literature. Several systems and load cells have been proposed that employ these optical devices to measure relative displacement of mechanical parts of the system through generation of electrical signals that are analogs of the load or force applied to the system or load cell. While these embodiments do not suffer from high stress fatigue as do the strain gauges, their displacements are all or in part angular and exhibit sin.crclbar. or cose errors. These optical systems also do not adequately address mechanical temperature coefficients of expansion and contraction because the mechanisms are not symmetrical.
Accordingly, it is one of the objects of the present invention to provide a parallel beam sensor apparatus that measures displacement of one beam in relation to another without exhibiting sin.crclbar. or cos.crclbar. errors.
Another object of the invention is to provide a parallel beam sensor apparatus in which parallel beams are mechanically interconnected in a manner to enable deflection of one beam without deflection of the other beam.
A still further object of the invention is the provision of a parallel beam sensor apparatus in which one of the beams is a load bearing beam that exhibits deflection in response to the application of force transverse to the long dimension of the load bearing beam and the other beam constitutes a stable plane of reference beam that does not move with the load bearing beam.
Yet another object of the invention is the provision of a parallel beam sensor apparatus in which corresponding ends of the parallel beams are interconnected in such a manner that a light source and slotted mask on one beam cooperate with light sensitive photodiodes on the other beam to measure and display the degree of relative transverse motion of one beam in relation to the other.
A further object of the invention is the provision of a parallel beam sensor apparatus that is a combination of mechanical and optical components configured to measure and display or record the relative transverse displacement of a load-bearing beam in relation to a non-load bearing beam by generation of an electrical current that is a linear analog of the load or force applied to the load-bearing beam.
The invention possesses other objects and features of advantage, some of which, with the foregoing, will be apparent from the following description and the drawings. It is to be understood however that the invention is not limited to the embodiment illustrated and described since it may be embodied in other forms within the scope of the appended claims.